java获取文件hash值_怎样用java获取到文件的hash值？

public static byte[] createChecksum(String filename) throws Exception {

InputStream fis = new FileInputStream(filename); //将流类型字符串转换为String类型字符串

byte[] buffer = new byte[1024];

MessageDigest complete = MessageDigest.getInstance("MD5"); //如果想使用SHA-1或SHA-256，则传入SHA-1,SHA-256

int numRead;

do {

numRead = fis.read(buffer); //从文件读到buffer，最多装满buffer

if (numRead > 0) {

complete.update(buffer, 0, numRead); //用读到的字节进行MD5的计算，第二个参数是偏移量

}

} while (numRead != -1);

fis.close();

return complete.digest();

}

public static String getMD5Checksum(String filename) throws Exception {

byte[] b = createChecksum(filename);

String result = "";

for (int i=0; i < b.length; i++) {

result += Integer.toString( ( b[i] & 0xff ) + 0x100, 16).substring(1);//加0x100是因为有的b[i]的十六进制只有1位

}

return result;

}